Apparatus for detecting light-transmissive sheet-like body

ABSTRACT

Illuminating light emitted from a light source is led via a condenser lens, an optical fiber, a half-silvered mirror, and a condenser lens to a reflector. The reflector reflects the illuminating light to a CCD device through a telecentric optical system which comprises the condenser lens, the half-silvered mirror, and an aperture member. The illuminating light applied to the CCD device is greatly reduced in amount as it passes through a light-transmissive sheet-like body twice. The light-transmissive sheet-like body itself or an edge thereof can be detected with high accuracy even if the light-transmissive sheet-like body has a high transmittance.

This is a continuation of application Ser. No. 10/060,148 filed Feb. 1,2002 now U.S. Pat. No. 6,943,363. The entire disclosure of the priorapplication, application number 10/060,148 is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for detecting alight-transmissive sheet-like body having a high transmittance or anedge thereof highly accurately.

2. Description of the Related Art

One known apparatus for detecting minute defects in a light-transmissivesubstrate made of glass or the like is shown in FIG. 1 of theaccompanying drawings (see Japanese laid-open patent publication No.2000-97867). The apparatus has a light source 2 for emittingilluminating light 4 and a telecentric optical system including acondenser lens 6 and an aperture member 8 for leading the illuminatinglight 4 to a CCD (Charge-Coupled Device) camera 10. When alight-transmissive substrate 12 having a defect is placed between thelight source 2 and the condenser lens 6, the defect in thelight-transmissive substrate 12 diffuses the illuminating light 4,changing the amount of transmitted light. The illuminating light 4 whichhas passed through the light-transmissive substrate 12 is led throughthe telecentric optical system to the CCD camera 10, which produces ahigh-contrast image of the defect.

While the conventional apparatus is capable of effectively detecting thedefect in the light-transmissive substrate 12, it is difficult for theapparatus to detect, with high accuracy, an edge 14 of thelight-transmissive substrate 12 or the light-transmissive substrate 12itself.

Specifically, if the transmittance of the light-transmissive substrate12 is large, then any difference between shadow and highlight areas ofthe image of the light-transmissive substrate 12 is very small. When thelight-transmissive substrate 12 vibrates while it is being detected orif the light-transmissive substrate 12 has transmittance variations, theaccuracy with which to detect the light-transmissive substrate 12 isgreatly reduced.

SUMMARY OF THE INVENTION

It is therefore a general object of the present invention to provide anapparatus for detecting a light-transmissive sheet-like body or an edgethereof stably with high accuracy.

An object of the present invention is to provide an apparatus fordetecting a light-transmissive sheet-like body whose edge can bedetected in emphasis.

Another object of the present invention is to provide an apparatus fordetecting a light-transmissive sheet-like body whose edge can bedetected with high accuracy without being adversely affected bypositional displacements of the light-transmissive sheet-like body.

Still another object of the present invention is to provide an apparatusfor detecting a light-transmissive sheet-like body whose length can bedetected with high accuracy.

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which preferredembodiments of the present invention are shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a conventional apparatus for detecting adefect in a light-transmissive substrate;

FIG. 2 is a schematic view of an apparatus for detecting alight-transmissive sheet-like body according to a first embodiment ofthe present invention;

FIG. 3 is a diagram showing the relationship between the angle ofincidence of illuminating light on a light-transmissive sheet-like bodyand the amount of light transmitted therethrough;

FIG. 4 is a view of an image of a light-transmissive sheet-like bodywhich is detected by the apparatus according to the first embodiment;

FIG. 5 is a schematic view of an apparatus for detecting alight-transmissive sheet-like body according to a second embodiment ofthe present invention;

FIG. 6 is a schematic view illustrating the manner in which the lengthof a light-transmissive sheet-like body is determined by the apparatusaccording to the second embodiment;

FIG. 7 is a flowchart of a process of calculating the length of alight-transmissive sheet-like body with the apparatus according to thesecond embodiment; and

FIG. 8 is a schematic perspective view of a film production system whichincorporates the apparatus according to the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 shows a basic arrangement of an apparatus 20 for detecting alight-transmissive sheet-like body according to a first embodiment ofthe present invention. As shown in FIG. 2, the apparatus 20 basicallycomprises a light source unit 22 for emitting illuminating light L, anoptical unit 26 (converging optical system) connected to the lightsource unit 22 by an optical fiber 24, a reflector 28 for reflecting theilluminating light L, and a CCD camera 30 (light detecting means) fordetecting the illuminating light L reflected by the reflector 28 with aCCD device 29 which serves as a two-dimensional area sensor, thereby toprovide two-dimensional information on the distribution of theilluminating light L. A light-transmissive sheet-like body 32 to bedetected is placed between the reflector 28 and the optical unit 26.

The light source unit 22 comprises a light source 34 for emitting theilluminating light L and a condenser lens 36 for converging theilluminating light L onto an end of the optical fiber 24.

The optical unit 26 comprises a half-silvered mirror 38 for reflectingthe illuminating light L outputted from the other end of the opticalfiber 24, a condenser lens 40 for converging the illuminating light Lreflected by the half-silvered mirror 38 into parallel-beamlight-transmissive light L and leading the parallel-beamlight-transmissive light L to the reflector 28, and an aperture member42 disposed at an image-side focal point of the condenser lens 40. Theoptical unit 26 comprises a telecentric optical system.

The apparatus 20 according to the first embodiment is basicallyconstructed as described above. Operation and advantages of theapparatus 20 will be described below.

The illuminating light L emitted from the light source 34 of the lightsource unit 22 is converged by the condenser lens 36, and led throughthe optical fiber 24 to the optical unit 26. In the optical unit 26, theilluminating light L is reflected by the half-silvered mirror 38,converged by the condenser lens 40 into parallel-beam light-transmissivelight L, which is led to the light-transmissive sheet-like body 32. Thelight-transmissive light L then passes through the light-transmissivesheet-like body 32, is reflected by the reflector 28, passes againthrough the light-transmissive sheet-like body 32, and reenters theoptical unit 26. In the optical unit 26, the light-transmissivesheet-like body 32 travels through the half-silvered mirror 38 and theaperture member 42 and is applied to the CCD device 29 of the CCD camera30, which detects the applied amount of illuminating light L and outputsan electric signal representing the detected amount of illuminatinglight L.

The illuminating light L which travels from the optical unit 26 to thereflector 28 and then back from the reflector 28 to the optical unit 26includes light transmitted through the light-transmissive sheet-likebody 32 and light bypassing the light-transmissive sheet-like body 32.Since the illuminating light L transmitted through thelight-transmissive sheet-like body 32 passes through thelight-transmissive sheet-like body 32 twice, the amount of theilluminating light L that falls on the CCD device 29 is greatly reduced.If any reflection by the surfaces of the light-transmissive sheet-likebody 32 is ignored, then the amount of illuminating light L which fallson the CCD device 29 is reduced at a rate of the square of thetransmittance of the light-transmissive sheet-like body 32. However, theilluminating light L bypassing the light-transmissive sheet-like body 32and falling on the CCD device 29 is not reduced in amount. Therefore, itis possible to determine whether the light-transmissive sheet-like body32 is placed between the optical unit 26 and the reflector 28 or notfrom the amount of illuminating light L detected by the CCD device 29.

FIG. 3 shows, for comparison, the transmittances (%) at various incidentangles θ of a single light-transmissive sheet-like body whosetransmittance at an incident angle θ of 0° is 70%, and thetransmittances (%) at various incident angles θ of twolight-transmissive sheet-like bodies whose transmittance at an incidentangle θ of 0° is 70%. It can be seen from FIG. 3 that the apparatus 20in which the illuminating light L passes through the light-transmissivesheet-like body 32 twice is capable reducing a greater amount ofilluminating light L than the conventional apparatus shown in FIG. 1 inwhich the illuminating light 4 passes through the light-transmissivesheet-like body 12 once. Therefore, the apparatus 20 can effectivelydetermine whether the light-transmissive sheet-like body 32 is placedbetween the optical unit 26 and the reflector 28 or not.

Since the apparatus 20 according to the first embodiment employs atelecentric optical system, the amount of illuminating light L which isdetected by the CCD device 29 differs greatly depending on whether thelight-transmissive sheet-like body 32 is placed between the optical unit26 and the reflector 28 or not, as shown in Table 1 below. Table 1shows, for comparison, detected levels of illuminating light L which isapplied directly to the CCD camera 20 after having passed through andbypassed the light-transmissive sheet-like body 32 whose transmittanceis 70% (general optical system+transmissive illumination: opticalcondition 1), detected levels of illuminating light L which is appliedto the CCD camera 20 via a telecentric optical system after havingpassed through and bypassed the light-transmissive sheet-like body 32(telecentric optical system+transmissive illumination: optical condition2, see FIG. 1), and detected levels of illuminating light L which isreflected by the reflector 28 and applied to the CCD camera 20 via atelecentric optical system after having passed through and bypassed thelight-transmissive sheet-like body 32 (telecentric opticalsystem+coaxial epi-illumination: optical condition 3, see the firstembodiment). It is assumed in Table 1 that the output signal produced bythe CCD camera 30 when a maximum amount of light falls on the CCD camera30 has a level of 255 and the output signal produced by the CCD camera30 when a minimum amount of light, i.e., no illuminating light L, fallson the CCD camera 30 has a level of 0.

TABLE 1 Light Optical Light passing bypassing Shadow − highlightconditions through sheet sheet difference Optical 125 150 25 condition 1Optical 114 156 42 condition 2 Optical 95 210 115 condition 3

In the optical condition 1 (general optical system+transmissiveillumination), the difference between detected signals produced when theilluminating light L passes through and bypasses the light-transmissivesheet-like body 32, i.e., the difference between shadow and highlightareas, has a level of 25. In the optical condition 2 (telecentricoptical system+transmissive illumination), the difference between thedetected signals has a level of 42. Accordingly, the telecentric opticalsystem is effective in making the resultant image clear. In the opticalcondition 3 (telecentric optical system+coaxial epi-illumination)according to the second embodiment, the difference between the detectedsignals has a much higher level of 115 due to a large amount ofilluminating light L which is reduced by the coaxial epi-illuminationarrangement. Consequently, the arrangement based on the telecentricoptical system+coaxial epi-illumination is capable of reliably detectingwhether the light-transmissive sheet-like body 32 is present or not eventhrough the light-transmissive sheet-like body 32 has a largetransmittance.

The apparatus 20 according to the first embodiment is also capable ofdetecting an edge 44 of the light-transmissive sheet-like body 32 withhigh accuracy as well as the light-transmissive sheet-like body 32itself. FIG. 4 schematically shows a two-dimensional image which isproduced by the CCD device 29 when the light-transmissive sheet-likebody 32 is positioned as shown in FIG. 2. The two-dimensional imageincludes an image 46 that is formed by the illuminating light L that haspassed through the light-transmissive sheet-like body 32 twice, an image48 that is formed by the illuminating light L that has bypassed thelight-transmissive sheet-like body 32 and been reflected by thereflector 28, and an image 49 that is formed by the edge 44 of thelight-transmissive sheet-like body 32.

Since the edge 44 refracts and diffuses the illuminating light L, theedge 44 is greatly effective to reduce the amount of illuminating lightL passing therethrough. Since the optical unit 26 comprises atelecentric optical system, the illuminating light L applied to the CCDdevice 29 is limited to principal light rays. Therefore, the image 49representing the edge 44 is lower in intensity than the image 46,allowing the edge 44 to be detected with high accuracy.

FIG. 5 schematically shows an apparatus 50 for detecting alight-transmissive sheet-like body according to a second embodiment ofthe present invention. Those parts of the apparatus 50 which areidentical to those of the apparatus 20 shown in FIG. 2 are denoted byidentical reference characters, and will not be described in detailbelow.

As shown in FIG. 5, the apparatus 50 comprises a light source unit 22for emitting illuminating light L, a pair of optical units 54 a, 54 b(converging optical systems) for leading the illuminating light L fromthe light source unit 22 to a reflector 28 via respective optical fibers52 a, 52 b, a pair of CCD cameras 56 a, 56 b (light detecting means) fordetecting the illuminating light L reflected by the reflector 28 via therespective optical units 54 a, 54 b, an image processor 58 (processingmeans) for processing images captured by the CCD cameras 56 a, 56 b, anda display monitor 60 for displaying the images processed by the imageprocessor 58.

The apparatus 50 thus constructed is capable of measuring, with highaccuracy, the length of a light-transmissive sheet-like body 32 which isplaced between the reflector 28 and the optical units 54 a, 54 b and fedin the direction indicated by the arrow.

The CCD cameras 56 a, 56 b capture respective images of an edge 44 ofthe light-transmissive sheet-like body 32 and an opposite edge 62thereof, and supply the captured images to the image processor 58. Theimage processor 58 displays the captured images on the display monitor60. The image processor 58 also calculates the positions of the edges44, 62 from the images, and determines the length of thelight-transmissive sheet-like body 32 from the calculated positions ofthe edges 44, 62. A process of determining the length of thelight-transmissive sheet-like body 32 will be described below withreference to FIGS. 6 and 7.

First, the light-transmissive sheet-like body 32 is introduced into apredetermined length measurement range. If a length measurement triggersignal is generated in step S1 shown in FIG. 7, then the image processor58 starts a process of detecting the edges 44, 62 of thelight-transmissive sheet-like body 32 in step S2. Specifically, theimage processor 58 scans the images captured by the CCD cameras 56 a, 56b in the direction in which the light-transmissive sheet-like body 32 isfed, and detects areas where the image density changes a predeterminedquantity as the edges 44, 62.

Thereafter, the image processor 58 calculates the coordinates of theedges 44, 62 in step S3. The coordinates are calculated by setting thecoordinates of the upstream ends of the CCD cameras 56 a, 56 b to “0”and determining coordinates from the coordinates “0” up to pixels wherethe edges 44, 62 are detected, as coordinates W1, W2 of the edges 44,62.

Using the coordinates W1, W2 of the edges 44, 62 thus determined, theimage processor 58 calculates the length X of the light-transmissivesheet-like body 32 in step S4. Specifically, if the distance between theimages captured respectively by the cameras 56 a, 56 b is indicated byX0 and the coordinates of the downstream ends of the images areindicated by W0, then the length X of the light-transmissive sheet-likebody 32 is determined as follows:X=W0−W1+W2+X0

If the values W0, W1, W2, X0 represent the numbers of pixels, then thevalue X is multiplied by the size of each pixel to determine the lengthX.

After the length X of the light-transmissive sheet-like body 32 isdetermined, the image processor 58 determines whether the length X isacceptable or not in step S5. Thereafter, the process is put to an end.

Since each of the optical units 54 a, 54 b comprises a telecentricoptical system which is telecentric on the object side, even if theposition of the light-transmissive sheet-like body 32 varies in thedirection of the optical axis of the telecentric optical system, theposition of the edge 44 can be detected highly accurately without beingadversely affected by the positional variation. Therefore, the length Xof the light-transmissive sheet-like body 32 can also be detected highlyaccurately.

FIG. 8 shows in perspective a film production system 70 whichincorporates the apparatus 50 shown in FIG. 5.

In the film production system 70, a roll film 72 of a rolledphotosensitive material is unwound and supplied from a film supply unit74, and cut into a succession of films F of given length by a filmcutting unit 76. The cut films F are then fed along a film feed line 78,sorted to an upper feed line 80 a and a lower feed line 80 b, and thensupplied to film stack producing devices 82 a, 82 b.

In each of the film stack producing devices 82 a, 82 b, films F arestacked on a protective cover 88 which is supplied from a protectivecover supply device 84 through a protective cover feed mechanism 86. Theproduced stack of films F is supplied to a stack reversing device 90 inwhich the stack is vertically reversed, i.e., turned upside down. Thestack of films F is then placed in a light-shielding package 94 in apackaged product manufacturing device 92, thus producing a packagedproduct 96. Packaged products 96 thus manufactured are stacked in apackaged product stacking device 98, and then shipped from the filmproduction system 70.

In the film production system 70 thus constructed, the apparatus 50 isdisposed on the film feed line 78. The film feed line 78 functions asthe reflector 28. The illuminating light L emitted from the light sourceunit 22 has a wavelength of 850 nm or higher because the films F are ofa photosensitive material sensitive to visible light.

The length of each of the films F supplied to the film feed line 78 isdetermined by the apparatus 50. If the determined length is notacceptable, then the film F is rejected as a defective film from thefilm feed line 78. Based on the determined length, the film F may besorted and supplied to the upper feed line 80 a or the lower feed line80 b.

Although certain preferred embodiments of the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

1. An apparatus for detecting a light-transmissive sheet-like body,comprising: a light source unit for emitting illuminating light; lightdetecting means for detecting the illuminating light; and an opticalsystem for leading the illuminating light as parallel-beam light to thelight-transmissive sheet-like body and converging the illuminating lightto said light detecting means, wherein an edge of the light-transmissivesheet-like body placed between said light source unit and said opticalsystem is detected based on a difference between two types ofinformation, said two types of information including information of saidilluminating light which is led to said light detecting means throughsaid edge and another information of said illuminating light whichbypasses said edge and is led to said light detecting means, and whereinsaid illuminating light passes twice through said light-transmissivesheet-like body.
 2. The apparatus of claim 1, wherein said lightdetecting means is oriented lengthwise parallel to a direction of travelof the light-transmissive body, to receive light which bypasses the edgeand to receive light which passes through said edge.
 3. The apparatus ofclaim 2, wherein said light detecting means detects light which bypassessaid edge and which passes through said edge, said edge comprising aleading edge of the light-transmissive body.